Electromagnetically driven assemblies can be operated in the so-called full stroke mode with low tolerance. Using the example of an injector for injecting fuel this operating mode means that during an injection process the needle of the injector moves up to a maximum deflection or an end position and that the mass of the injected fuel is varied by varying the duration of the electric actuation of a coil drive of the injector. This duration determines the injection time, which in turn determines the mass of the fuel which is injected or is to be injected.
A trend toward relatively small injection quantities accompanied by a simultaneously relatively high static fuel throughflow rate has led to an increase of the so-called ballistic operating mode of injectors. The ballistic injector operating mode includes a partial deflection of the injector needle in a trajectory which is predefined by electrical and constructive parameters and is free, or parabolic, after the ending of the application of magnetic force, before reaching the full stroke length. In contrast to the full stroke, the ballistic operating mode of the injector is significantly more affected by tolerances, since here both electrical and mechanical tolerances of the respective injector have a significantly greater influence on the movement profile of the injector needle than is the case in the full stroke mode.
A compensation of such injector tolerances is described, for example, in DE 38 43 138 A1 for a coil-based injector. In this context, an individual measurement of a voltage profile is carried out for each injector, which voltage profile is superimposed on the profile of the actual actuation of the respective injector and depends on the individually electrical and also mechanical properties of the respective injector. The compensation described in DE 38 43 138 A1 is based on the fact that an unavoidable feedback signal occurs at coil-operated assemblies, which feedback signal depends, by means of a coupling driven by an eddy current, between the mechanics of the injector (armature and injector needle) and the magnetic circuit (coil) of the injector. Therefore, the time profile of this feedback signal depends on the actual movement behavior of the injector needle of the respective injector.